In general, foodstuffs are prepared from agricultural products, marine products, livestock products, etc. However, during the course of storage or preservation processing of raw food materials or products, raw food materials or products are deteriorated by contamination and putrefaction with microorganisms or by chemical or physical action to reduce their commercial value. Therefore, a variety of food additives have been developed and at the same time, methods for a temperature treatment, an oxygen absorption treatment, vacuum packaging, low temperature storage, a radiation treatment, etc. have been developed and practically used.
The most serious problem in such deterioration of food materials or products is oxidation or peroxidation of food ingredients with oxygen in the air. Oxygen maintains life of the living thing through respiration. On the other hand, it is known that oxygen is a very reactive compound so that it reacts with various ingredients in food to oxidize or peroxidize the ingredients thereby to not only reduce their commercial value but also form injurious materials in food. It is reported that for example, nutritionally required unsaturated fatty acids such as linoleic acid, linolenic acid, etc., which are contained in foods, are readily peroxidized by oxygen in the air to form peroxidized fatty acids or reactive radicals (free radicals) and at the same time, form carcinogenic substances such as malone dialdehyde, etc. It is also reported that peroxidized lipids formed by peroxidation of unsaturated fatty acid molecules in lipids modify protein or nucleic acid in vivo to cause the living body in its carcinogenic action, etc. ("Mutagen and Toxicity", vol. 5, page 243 (1982), "Packaging of Food", vol. 17, page 106 (1986)).
In order to prevent such peroxidation of lipids, techniques for packaging such as removal of oxygen in the package with a free oxygen absorber, vacuum packaging, nitrogen gas substitution packaging, etc. have been used. On the other hand, synthetic antioxidants, for example, butylhydroxyanisole (BHA), butylhydroxytoluene (BHT), etc. have been generally used, backed by development of chemical industries. However, as use of such synthetic antioxidants increases, food pollution increases and a serious problem occurs in view of safety. It is thus the actual situation that the consumer's rejection against synthetic antioxidants has been increasing and its amount of use decreases.
On the other hand, it is considered that peroxides or carcinogenes formed in animal living body would adversely affect animal cells due to the toxic action of oxygen as described above. Such peroxidation of vital components with oxygen would be correlated to aging of cells and thus to a life span (theory of free radical aging). Therefore, highly safe antioxidants derived from the natural world have been greatly expected to be substances for supporting the antioxidative protective mechanism in vivo, not only in foodstuffs, especially health maintaining foods or nutrient foods, but also in the technical fields of medicines and cosmetics.
However, the only natural antioxidants that have been expected to be practically used in place of synthetic antioxidant involving problems in food pollution are vitamin C prepared by chemical synthesis and vitamin E (tocopherol) extracted and purified from natural products.
In order to suitably use such antioxidants derived from the natural world for use in foods, drugs, cosmetics, etc., it is important to find natural antioxidants having different properties and utilize the antioxidants under such conditions that their characteristics are exhibited.
A variety of compounds having an antioxidative activity are contained in spices derived from plants and, spices have been added to food as having an action of preserving foods (Packaging of Food, vol. 19, No. 1, page 97, 1987). However, most of spices exhibit a strong flavor or color. In order to add these spices to foods, drugs, cosmetics, etc. as antioxidants or the like, such properties have automatically limited their use range.
Vitamin C is insoluble in fat or lipids in vivo since it is a water soluble substance. On the other hand, vitamin E is insoluble in an aqueous solution such as blood, etc. and accumulated in lipids in vivo, since it is fat-soluble. Such properties of extreme water solubility and fat solubility are not considered to be necessarily advantageous, in the case of foods, drugs, cosmetics, etc. applied to the living body. In order to exhibit their antioxidative activity appropriately in any of lipids and aqueous solutions in vivo, natural substances having an intermediate property between water solubility and fat solubility are advantageous.
In addition to vitamin C or vitamin E, extensive investigations have been made on properties of natural antioxidants derived from spice plants, and reports are made thereon.
However, natural antioxidants other than natural vitamin E, vitamin C, etc., that are expected to be used in place of synthetic antioxidants involving problems in food pollution have not been practically utilized, because their origins are plants or animals affected by natural conditions such as weather, etc. and it is thus difficult to stably supply them, their contents are extremely a trace amount, extraction may be made only with extreme difficulty, and components change during extraction.
A potent antioxidative activity is noted in sesame oil obtained from seeds of Sesamum indicum L. by lignan compounds modified during the course of purification of sesame oil. Thus, sesame oil has been given an important position as an excellent edible oil which is not deteriorated by oxidation ("Grand Modern Encyclopedia", Gakushu Kenkyusha (Jan. 1, 1979), pages 123-124).
On the other hand, it is already known that not only sesame oil is contained in Sesamum indicum L. contains but also antioxidants such as vitamin E or lignan compounds, etc. are contained in the plant body of sesame (Agricultural and Biological Chemistry, vol. 49, page 301 (1985)), Journal of the Japanese Food Industry Association, vol. 32, page 407 (1985)). However, it is quite unknown or not even suggested that growing cells from sesame plants, especially cells grown at a high temperature can be industrially cultivated, a glycoside substance having a potent antioxidative activity is contained in these growing cells, and the substance can be efficiently extracted and produced industrially without causing any denaturation or deterioration.